The present invention relates to improvements in an electrophotographic copier.
In general, an image is formed in this kind of copier in such a manner that: a document placed upon a platen glass is exposed to light emitted by a lamp for document-image reading use; an electrostatic latent image is formed by the reflected light on a photoreceptor drum, on the surface of which a photoconductive material such as an organic photosensitive material is coated; the electrostatic latent image is developed by a developing section so that a toner image can be formed; the toner image is transferred onto a recording paper; and the transferred image is thermally fixed by a fixing section.
In a conventional copier, when a platen glass is heated to more than a predetermined temperature by a lamp for document-image reading use, there is a possibility that an operator of the copier is psychologically and physically damaged by the heat of the lamp. Especially, in the case of an electrophotographic copier to be sold in U.S.A., a raise in temperature is strictly regulated by the requirements of the UL Standards. Therefore, the following countermeasures are adopted for a conventional copier:
(1) Temperature of the platen glass is measured sensor, and when the measured temperature exceeds a predetermined value, the value of CPM (which is the number of copied papers per unit time) is lowered. PA0 (2) According to the copying magnification, the value of CPM is lowered so that it can be a predetermined value which has been previously set. PA0 In the case of (1) in which the temperature sensor is utilized, the cost and man hour are increased, and the apparatus becomes complicated. PA0 In the case of (2) in which the value of CPM is determined according to the copying magnification, there is a possibility that the processing speed is unnecessarily lowered and the performance of the apparatus can not be exhibited.
However, in the aforementioned conventional image forming apparatus, there are problems which will be described as follows: